400ex motor needs a rebuild i need help deciding!!!!

[trailrider91]

The motor in my 400ex needs a rebuild. I want more power so I was going to do a port and polish a hot cam and I would like to do a big bore. Also I was wondering about a 450 carb. If I do all this will I see a good increase in power? This is all new to me any help is appreciated thank you!!!!

[quadmanw]

That'd be a great increase in power. Is it already built? If not I'd go like this:

Stage 2 hot cam
11:1 wiseco piston
P&P
450r carb
Grinded header welds
Open air box and run uni
GTT head studs to be safe
And bore to a 407 or 416(cant remember the mm)

This seems to be the most reliable build around here and almost everyone uses it.

[trailrider91]

What about a 426?

[quadmanw]

Yeah, you could do a 426. I don't think you would see that much more power unless you uped the compression to a 12.5:1 piston. Power comes from compression not as much from bore size unless you go to a 440

[quadmanw]

Also if you go any higher than 11:1 on the compression you will need to run race gas. Which isn't always convenient

[trailrider91]

So if I do 11:1 stage 2 hot cam some p and p head studs and a 450 carb and air filter ill see a good increase?

[trailrider91]

Also does anyone have a recomendation for a head and slip on set up? What does ground header welds mean ? This is all new to me ive been around cars my whole life and just got into quads so I don't want to sound dumb. Thanks everyone

[quadmanw]

Don't bother with a header. You're wasting you're money. Take your headers off and right where they meet the jug there is welds in there. They can be ground down for more air flow. Also IMO the motoworks pipe is the best. They're only like $200 bucks and they have a great sound and good power. I've been running one for years now. I bought it back when they coated $300 lol. There are many posts and pics on the forum about the ground down welds

[trailrider91]

Awesome thank you!!! So ill do a 416 head studs stage 2 cam crf cam chain p and p and a 450 carb. Thanks so much

[trailrider91]

When people use the 450 carb do they use the crf or the trx ones?

[quadmanw]

The trx. Crf Is Hondas dirt bike lol. We use the Crf timing chain tho

[TheAwesomehonda]

Hey man if you have questions about the bore and compression just read this first. http://www.exriders.com/vbb/showthread.php?s=&threadid=487458

[trailrider91]

How hard is it to get a 450 carb to fit

[trailrider91]

Alright I've decided on 416 and a hot cam and crf chain and studs. Anyone have any advice as far as this goes?

[quadmanw]

That's a good setup, I just rebuilt mine to that. You will be very happy if your mechanic does it right

[trailrider91]

I need valve seals so I'm having a place do that and bore the jug but I'm doing the assembly myself. So I'm pretty excited!!! Now what do I need to do as far as jettng goes?

[quadmanw]

Every bikes different and mine jetting is in my signature. If I were you I'd ask Marc(CJM). He helped me with mine and he knows what he's talking about. Real good guy. Lol :blah:

[CJM]

do the 407, the 416 will not make any more power than the 407. Compression makes power. Your only wasting bore sizes with a larger bore and should you go that route you wind up like me, Im now at a 426 and canonly do a 440 or go back to a stock sized sleeve and bore it for my old 416 piston or run a stock sized piston. Compression is the reason I can eat alive a 440 as most of them are pretty low compression.

As for valve seals, honda ones are fine. You will need a valve compressor to do the job. its not very hard, I use a tusk brand one. You will also want to lap the valves with grinding compound and a drill. Google it, super easy.

As for the right build, easy (hell I should sticky it as EVERYONE seems to use this build steve and I came up with lol).

This is the setup and trust me it will make ALOT of power over stock.

You should also take a peek at the timing chain, chain tensioner and chain guides while you got it apart. Check the guides for wear, replace the chain anyways and check the tensioner.


Originally posted by quadmanw
That'd be a great increase in power. Is it already built? If not I'd go like this:

Stage 2 hot cam
11:1 wiseco piston
P&P
450r carb
Grinded header welds
Open air box and run uni
GTT head studs to be safe
And bore to a 407 or 416(cant remember the mm)

This seems to be the most reliable build around here and almost everyone uses it.

[trailrider91]

407 it is!! You guys are awesome very helpful. Is there anything I can do for cooling or anything to help? Also I can't find anything about the header welds and I want to do that. Or is that self explanatory

[Stickman400]

Most guys on here run a CFM or UM Performance oversized oil tank and a SPAL fan that's mounted to the oil cooler to help it run cooler. Jetting it correctly will also keep it cool.

[quadmanw]

This was my rebuild. There's a picture or two of the grinds down welds in the header. Also maybe some things or pics will help you with your build

[quadmanw]

Forgot to add it.. Lol, sorry

http://exriders.com/vbb/showthread.php?s=&threadid=483582&perpage=10&pagenumber=5

[trailrider91]

How hard would it be to do a Minot port and polish myself? I understand the concept of it. Any input?

[quadmanw]

I wouldn't do that... But that's just my opinion lol. There is a lot more to it than just getting rid of excess stuff